Many communication devices operate on battery power. The radiotelephones in use today are almost all portable devices utilizing rechargeable batteries that need periodic recharging. The size of the battery and the power efficiency of the communication device determine the amount of talk time available to a user. As a convenience to a user, it has always been desirable to extend the life of the battery to provide longer talk times. However, even with current devices, communications are occasionally interrupted, requiring the recharging of the battery or replacement with a freshly recharged battery. Therefore, it has been desirable to extend the battery life on a communication device.
In most cases, the largest drain on battery power is the transmitter of the communication device, followed by the receiver. The transmitter, or more specifically the power amplifier of the transmitter, in a communication device has typically been configured so that it only draws power when the user wishes to transmit. As the user controls the transmission time, and the amount of power transmitted is controlled by standard, the current drain drawn on a battery from the transmitter circuit has already been limited to those times and amounts that are strictly necessary for communication. However, the power used by the receiver is less controlled. For example, the receiver must be ready to receive an incoming call that may occur at any time. For this to happen, the receiver must be on, drawing power, and ready to receive.
Receiver operation is different in different operating systems. For example, in Time Division Multiple Access (TDMA) systems or Global System for Mobile (GSM) communication systems, the receiver operation is time-gated such that it is powered down (sleeps) during those known times when messages can not be received (i.e. no messages can be transmitted). In other words, the receiver only operates at a particular time when messages can be received. Other communication systems, in practice, may require the receiver to be on continuously. One example of such a specification is Telecommunications Industry Association/Electronic Industry Association (TIA/EIA) Interim Standard Is 95, “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (IS-95). IS-95 defines a direct sequence code division multiple access (DS-CDMA or CDMA) radiotelephone system. In a CDMA system, the communication device can transmit in a gated fashion, depending on the requited data to be transmitted. In addition, bursting the transmitter decreases battery current drain, increasing talk time. However, due to the full duplex nature of CDMA, the receiver must be on continuously in order to receive incoming data while on a traffic channel.
One prior art method to reduce some receiver on-time in a CDMA system is slotted paging mode. Slotted paging mode is a special form of discontinuous reception (DRX) operation for a battery-operated mobile radio such as a cellular radiotelephone while in paging mode. In slotted paging mode, when the radiotelephone is in an idle mode (i.e., not engaged in a call), the radiotelephone does not continuously monitor a paging channel. The goal of slotted paging mode operation is to reduce the on-time of the radio during paging mode by powering-off portions of the radio, such as the receiver, during idle (sleep) periods. In the idle state, the radiotelephone wakes up only during slots preassigned by the radiotelephone system or to process some other condition, such as a user input. However, this type of receiver operation is only operable in paging mode, and requires resynchronization procedures to be implemented upon powering-up the receiver. Moreover, a timing reference must be maintained during these sleep modes, which itself dissipates power. Further, the radiotelephone may also be required to wake up to process or respond to other events occurring asynchronously in the radio, in addition to exiting a sleep mode during assigned slots. None of these address receiver power control during calls.
Accordingly, there is a need for a method and apparatus for reducing current drain in a communication device such as a radiotelephone while operating on a traffic channel. There is a further need to reduce the current drain by the receiver in a communication device operating in a CDMA system, without sacrificing the ability to receive incoming signals. It would also be of benefit to provide these advantages without additional hardware, which would increase the cost of the communication device.